Adjustable blinds are commonly used in both commercial and residential buildings. The style of blind used in each building may be chosen from a variety of different styles and colours and may be chosen for aesthetic, economic and/or privacy reasons. Typically the blinds include a plurality of vertical or horizontal slats which are connected together. The slats are synchronously adjustable between a closed position, where adjacent slats overlap to block out the light, and a fully open position, where the slats parallel to each other and generally perpendicular to the plane of the window so the maximum amount of light is admitted into the room through the blind. Intermediate positions may be used to vary the amount of light allowed past the blind.
It is well known that the intensity of the sun may increase the temperature inside a building such that it is required to air condition the building. Even during the winter months in cold climates it is still necessary, in some instances, to air condition due to the increased heat caused by the intensity of the sun. Accordingly it is desirable to provide window blinds that are adjustable so that the windows can be totally or partially covered during the heat of the day to help control the temperature in the room. Further, it is desirable if these adjustments are done automatically without human intervention.
Various devices for automatically opening and closing blinds have been proposed. Typically these devices include control systems, which are either open loop or closed loop systems, connected to a blind.
Open loop systems operate by comparing the input signal with a predetermined reference level. The input signal is obtained from a sensor which measures the light intensity or temperature or both. There are typically two predetermined levels, one for a light threshold and the other for a dark threshold. When the input signal is above or below the predetermined levels a motor is actuated until a limit switch prevents further travel and accordingly the blind is either opened or closed respectively. For example, U.S. Pat. No. 2,962,647 issued to Borenstein on Nov. 29, 1960; U.S. Pat. No. 3,294,150 issued to Thomas on Dec. 27, 1966; U.S. Pat. No. 4,727,918 issued to Schroeder on Mar. 1, 1988; and U.S. Pat. No. 4,864,201 issued to Bernot on Sep. 5, 1989 show open loop systems. One drawback of all open loop systems is that inherently they only have two positions corresponding to the blinds being fully opened or fully closed.
Closed loop systems differ from open loop systems in that they inherently have the ability to have a number of output positions. Closed loop systems operate by sensing the light level within a room and moving the window covering to control the amount of light which enters the room. These systems include a feedback loop as part of the control system. Two such systems are shown in U.S. Pat. No. 3,294,152, issued to Kuijvenhoven on Dec. 27, 1966; and U.S. Pat. No. 3,646,985, issued to Klann on Mar. 7, 1972. These two systems include a light sensor as part of the feedback loop which measures the light intensity in the room and feeds this signal back to the control circuitry. Both of these systems use limit switches to set the position of the blind including the extreme open and closed positions.
It is desirable to have a system that rather than monitoring the light level in a room, monitors or senses the light at the outside of the blind and then sets the position of the blind. With a system that sets the position of the blind, the system may be designed so that a person in the room can easily adjust the system to meet their lighting needs. Further, it is desirable to provide a system having an optional safety feature in which at night the blinds are fully closed. Further, it is desirable to provide a system wherein there is a large variety of positions for the blind.
Taken alone or in combination none of the above mentioned prior art systems teach a system that sets the position of the blind based on the intensity of the sunlight, that a user can easily adjust the position of the blind, that has a closed position in the dark, and that has a large variety of positions.